如何可靠地确定 System.Windows.Forms.MonthCalendar 控件的 PreferredSize？

Question

在我的表单上，我有一个System.Windows.Forms.TableLayoutPanel，其中我将System.Windows.Forms.Panel 设置为DockStyle.Fill，在面板中，有一个System.Windows.Forms.MonthCalendar 控件（也设置为填充）。

日历是一个继承的控件，只是为了允许覆盖主题，以便我可以设置颜色等。继承的部分来自另一个我已经忘记的 SO 问题。

代码：

public class NativeMethods
{
    [DllImport("uxtheme.dll")]
    public static extern Int32 SetWindowTheme(IntPtr hWnd, String appname, String idlist);
}

public class CustomMonthCalendar : MonthCalendar
{
    public CustomMonthCalendar()
    {
        InitializeComponent();
        Margin = new Padding(0);
    }

    private void InitializeComponent()
    {
        SuspendLayout();
        ResumeLayout(false);
    }

    protected override void OnHandleCreated(EventArgs e)
    {
        NativeMethods.SetWindowTheme(Handle, String.Empty, String.Empty);
        base.OnHandleCreated(e);
    }
}

public class CustomCalendar : UserControl
{
    DayPickerControl = new CustomMonthCalendar();
    DayPickerControl.ForeColor = SystemColors.ControlText;
    DayPickerControl.BackColor = BackgroundColor;
    DayPickerControl.TitleForeColor = TextColor.Lighten(1.2f);
    DayPickerControl.TitleBackColor = BackgroundColor;
    DayPickerControl.TrailingForeColor = Color.Gray;
    DayPickerControl.Dock = DockStyle.Fill;
    DayPickerControl.FirstDayOfWeek = Day.Sunday;
    DayPickerControl.Font = new Font("Microsoft Sans Serif", 9f, FontStyle.Regular);
    DayPickerControl.MaxDate = new DateTime(2999, 12, 31, 0, 0, 0, 0);
    DayPickerControl.MaxSelectionCount = 7;
    DayPickerControl.MinDate = new DateTime(1900, 1, 1, 0, 0, 0, 0);
    DayPickerControl.ScrollChange = 1;
    DayPickerControl.SetCalendarDimensions(1, 1);
    DayPickerControl.ShowToday = true;
    DayPickerControl.ShowTodayCircle = true;
    DayPickerControl.Text = null;

    DayPickerPanel = new Panel();
    DayPickerPanel.BorderStyle = BorderStyle.None;
    DayPickerPanel.Dock = DockStyle.Fill;
    DayPickerPanel.Location = new Point(0, 0);
    DayPickerPanel.Padding = new Padding(2);
    Size prefSize = DayPickerControl.GetPreferredSize(new Size(200, 200));
    DayPickerPanel.Size = new Size(prefSize.Width + 5, prefSize.Height + 5);
    DayPickerPanel.Paint += panelBorder_Paint;
    DayPickerPanel.Controls.Add(DayPickerControl);
}

所以问题在于确定日历控件想要的大小。不管我做什么，我从GetPreferredSize() 得到的尺寸总是178, 155。然而，在屏幕上，日历的右侧边缘被截断，这意味着它比它停靠的面板大。这向我表明，它可能也不太关心停靠。不确定。

我摆弄了各种停靠/取消停靠与锚定设置，但结果总是相同。

为什么我的尺寸看起来不正确？以及如何确定适合它的正确尺寸？

编辑：使用 Hans Passant 的建议，我得出了这个解决方案：

//A new event in the CustomMonthCalendar class
public event EventHandler<AfterHandleCreatedArgs> AfterHandleCreated;

//A modified version of the OnHandleCreated() method shown above (add event call)
protected override void OnHandleCreated(EventArgs e)
{
    NativeMethods.SetWindowTheme(Handle, String.Empty, String.Empty);
    base.OnHandleCreated(e);
    if (this.IsHandleCreated && AfterHandleCreated != null)
        AfterHandleCreated(this, new AfterHandleCreatedArgs(new Size(this.Size.Width + 5, this.Size.Height + 5)));  //cosmetic padding
}

//A new class for the event args it passes...
public class AfterHandleCreatedArgs : EventArgs
{
    private Size _newSize = Size.Empty;
    public Size NewSize { get { return _newSize; } set { _newSize = value; } }

    public AfterHandleCreatedArgs(Size newSize)
    {
        _newSize = newSize;
    }
}

//And a handler to attach to that new event (in CustomCalendar class)...
private void DayPickerControl_AfterHandleCreated(Object sender, AfterHandleCreatedArgs e)
{
    if (!e.NewSize.Equals(Size.Empty))
        DayPickerPanel.Size = e.NewSize;
}

Answer 1

MonthCalendar 是一个“难”的控件。它用于 Windows 中高度可见的区域（时钟），因此在 Windows 版本之间进行了相当多的修改。它不可调整大小，并且它的大小因版本而异。

所以，不，使用 Dock = Fill 肯定行不通，这需要控件可调整大小。 GetPreferredSize() 只能返回一个猜测值，它可能曾经在旧 Windows 版本上是正确的，但现在不是。

您需要处理它的行为。直到创建控件的本机窗口之后，您才能知道它的真实大小。通常在表单的 Load 事件或控件的 OnCreateHandle() 方法中（如果您从它派生）。此时它的 Size 属性将是可靠的。您需要相应地调整其父控件。

Answer 2

您可以通过询问日历的句柄来强制调整日历的大小：

IntPtr h = calendar.Handle;